The Blades were guaranteed a top-six finish before kick-off but the point lifted them into fifth place above Swindon to set up a two-legged tie with Yeovil in the semi-finals.
United substitute Chris Porter had a 62nd-minute strike chalked off for handball, while Preston midfielder Lee Holmes clipped the crossbar with the visitors' best chance.
"Anybody who has finished in the top six deserves to be there and whoever we'd have got it was going to be a tough task," said caretaker boss Morgan. "Yeovil beat us here earlier in the season and I thought they were excellent. They had a great team-work ethic, so I'll have a look at the DVD of that game and look where their strengths and weaknesses were - as we do for every game.
"What I've said to the players in there is: 'congratulations on securing a playoff place', because we've had to work damned hard this year to get that.
"A club of this size, everyone always thinks your budget is massive but that's not the case. We've had a group of players this year who've worked really hard and hung on chasing automatic promotion - so I think to secure a play-off place this season, the players deserve it.
"They've had a fantastic reaction from losing the play-off final last year, to come back and be as hungry again to be promoted."
The draw leaves the Blades with just one win from their last eight games but Morgan insists he is not worried about form going into the play-offs.
"I'm not worried about it at all," he said. "Look at the Champions League this week, you get Munich and Dortmund, who were potentially playing two of the best European teams for years in Real Madrid and Barcelona, and look at the results they got.
"For me, you go into a knockout competition and it's whatever team holds its nerve and is strong enough to see the job through."